Fan structure

ABSTRACT

A fan structure includes a hub and a plurality of blades extending from the periphery of the hub. The airflow generated by the fan forms a boundary layer on the surface of each blade. The present invention is characterized in that: each of the blades is provided with a plurality of polygonal dents, a turbulent flow is generated in each dent when the airflow passes through the dent, a plurality of the turbulent flows collect together to form an air film between the surface of blade and the boundary layer. By this structure, the distance of separating points from the boundary layer is extended, and the frictional force and noise caused by the rotation of the blades are reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fan, in particular to a fan structure which is capable of reducing an aerodynamic drag.

2. Description of Prior Art

A conventional heat-dissipating system applied to a computer host or other electronic apparatus includes a heat-dissipating fan for generating compulsive airflow for dissipating the heat to the outside. Since the heat-dissipating fan operates for a long period of time, the heat-dissipating effect thereof is much relevant to its operating efficiency. On the other hand, if the noise generated by the heat-dissipating fan is too large, the user will feel very uncomfortable.

In general, airflow is generated when a fan rotates. The airflow forms a thin layer, referred to as a boundary layer, when it passes through the surface of blades of the fan. The boundary layer of airflow may generate turbulent flows beyond separating points where the airflow separates from the blades. The turbulent flows may cause the blades to vibrate and thus generate undesirable noise. Further, due to the turbulent flows, a frictional force may generate between the surface of the blade and the airflow, which deteriorates the rotating efficiency of the fan. According to experimental data, controlling a flow field is one method for reducing the frictional force and extending the distance of the separating points from the boundary layer. Thus, it is an important issue for the present Inventor to change the flow field around the surface of an article so as to reduce the frictional force.

In view of the above, the present Inventor proposes a reasonable and novel structure based on his research and expert knowledge.

SUMMARY OF THE INVENTION

The present invention is to provide a fan structure, which is capable of reducing a frictional force and noise generated by the fan.

The present invention is to provide a fan structure, whereby the rotation of blades is smoother, labor-saving and power-saving, and the heat-dissipating efficiency of the fan is increased.

The present invention is to provide a fan structure including a hub and a plurality of blades extending from the periphery of the hub, the airflow generated by the fan forming a boundary layer on the surface of each blade, characterized in that: each of the blades is provided with a plurality of polygonal dents, a turbulent flow is generated in each dent when the airflow passes through the dent, and a plurality of the turbulent flows collect together to form an air film between the surface of blade and the boundary layer.

The present invention is to provide a fan structure, in which the periphery of a casing is formed with recessed portions recessed toward an accommodating space in the fan. With this arrangement, more external air can be introduced into an intake side and the exhaust resistance generated on an exhaust side can be lowered.

The present invention is to provide a fan structure, in which the polygonal dents provided on the surface of each blade is formed into a shape selected from a group constituting of triangle, quadrangle, pentagon, hexagon, heptagon and octagon. With this arrangement, the fan can generate turbulent flows in each polygonal dent at different rotating speeds.

In comparison with prior art, the fan structure of the present invention is provided on the blade with a plurality of polygonal dents. When the airflow passes through the surface of each blade, the airflow is brought into contact with the periphery of each polygonal dent to generate a turbulent flow. The turbulent flow stays in the polygonal dent. A plurality of the turbulent flows collect together to form an air film for separating the surface of the blade from the boundary layer. Since the air film can extend the distance of the separating points from the boundary layer to thereby prevent the generation of the turbulent flows near the blades, the noise and the frictional force generated by the turbulent flows can be reduced. Therefore, the rotation of the blades is smoother, labor-saving and power-saving, and the heat-dissipating efficiency of the fan is increased.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is an assembled perspective view showing the external appearance of the fan according to the present invention;

FIG. 2 is a perspective view showing the external appearance of the hub and the blades according to the present invention;

FIG. 3 is an assembled cross-sectional view showing the hub and the blades according to the present invention;

FIG. 4 is a schematic view showing the airflow generated by the fan according to the present invention;

FIG. 5 is a schematic view showing the relationship between the blade and the airflow generated by the fan according to the present invention; and

FIG. 6 is a schematic view showing the blade according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description and technical contents of the present invention will become apparent with the following detailed description accompanied with related drawings. It is noteworthy to point out that the drawings is provided for the illustration purpose only, but not intended for limiting the scope of the present invention.

Please refer to FIGS. 1 to 3. The present invention provides a fan 1, which includes a casing 10, a hub 20 and a plurality of blades 30 extending from the periphery of the hub 20.

The casing 10 is formed into a square frame and has an accommodating space 100 therein. The hub 20 and the plurality of blades 30 are combined in the accommodating space 100. The casing 10 comprises an intake side 11 and an exhaust side 12 opposite to the intake side 11. The peripheries of the intake side 11 and the exhaust side 12 are formed with a recessed portion 13 respectively which is recessed toward the accommodating space 100. In the present embodiment, four recessed portions 13 are provided, and each recessed portion 13 is provided in the center of each side of the casing 10.

The hub 20 and the blades 30 extending from the periphery of the hub 20 are combined in the accommodating space 100. The interior of the hub 20 has a shaft 21 and a motor (not shown). The motor drives the shaft 21 of the hub 20 to rotate, which causes the blades 30 provided at the periphery of the hub 20 to rotate accordingly to thereby generate airflow.

Each of the blades 30 comprises a first surface 31 and a second surface 32 opposite to the first surface 31. Each of the blades 30 is provided on its surfaces with a plurality of polygonal dents 33. These polygonal dents 33 may be formed into any one shape selected from the group constituting of triangle, quadrangle, pentagon, hexagon, heptagon and octagon. Thus, two adjacent sides of the polygonal dent 33 form an angle. In the present embodiment, the first surface 31 and the second surface 32 of the blade 30 are provided with the polygonal dents 33. In practice, the polygonal dents 33 may be only provided on the first surface 31 or the second surface 32.

Please refer to FIGS. 4 and 5. FIG. 4 is a schematic view showing the airflow generated by the fan according to the present invention, and FIG. 5 is a schematic view showing the relationship between the blade and the airflow generated by the fan according to the present invention. When the fan 1 rotates, the recessed portions 13 are configured to facilitate more external air to be introduced into the intake side 11. When the airflow is exhausted from the exhaust side 12, the recessed portions 13 are configured to lower the exhaust resistance of the airflow.

The airflow A generated by the fan 1 forms a boundary layer B on the surface of each blade 30. On the other hand, when the airflow A passes through the periphery of each polygonal dent 31, the airflow A generates a turbulent flow T in the polygonal dent 33. Many turbulent flows T collect together to form an air film between the surface of the blade 30 and the boundary layer B. The air film can extend the distance of separating points S from the boundary layer B, so that the separating points S are formed outside the blade 30. With this arrangement, the generation of the turbulent flows can be prevented in the vicinity of the blades 30, whereby the noise and the frictional force caused by the turbulent flows can be reduced.

In the above structure, the turbulent flow T is often generated at the periphery of each polygonal dent 33. Further, when the speed of the airflow A increases, the turbulent flow A can be generated more easily. Thus, when the speed of the airflow A is larger, each of the polygonal dents 33 may be formed into a shape of fewer sides such as a triangle or quadrangle shape. Contrarily, when the speed of the airflow A is smaller, each of the polygonal dents 33 may be formed into a shape of more sides such as a hexagon or heptagon shape.

Please refer to FIG. 6, which shows the second embodiment of the present invention. The difference between the second embodiment and the first embodiment lies in that: the polygonal dents 33 a on the blade 30 a may be formed into at least two shapes selected from the group constituting of triangle, quadrangle, pentagon, hexagon, heptagon and octagon.

Although the present invention has been described with reference to the foregoing preferred embodiments, it will be understood that the invention is not limited to the details thereof Various equivalent variations and modifications can still occur to those skilled in this art in view of the teachings of the present invention. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims. 

1. A fan structure including a hub and a plurality of blades extending from the periphery of the hub, the airflow generated by the fan forming a boundary layer on the surface of each blade, characterized in that: each of the blades is provided with a plurality of polygonal dents, a turbulent flow is generated in each dent when the airflow passes through the dent, and a plurality of the turbulent flows collect together to form an air film between the surface of blade and the boundary layer.
 2. The fan structure according to claim 1, further including a casing, the casing being formed into a square frame and having an accommodating space, the hub and the blades being combined in the accommodating space.
 3. The fan structure according to claim 2, wherein the periphery of the casing is formed with at least one recessed portion recessed toward the accommodating space.
 4. The fan structure according to claim 1, wherein two adjacent sides of the polygonal dent form an angle.
 5. The fan structure according to claim 1, wherein each of the polygonal dents is formed into any one shape selected from the group constituting of triangle, quadrangle, pentagon, hexagon, heptagon and octagon.
 6. The fan structure according to claim 1, wherein each of the polygonal dents on the blades is formed into at least two shapes selected from the group constituting of triangle, quadrangle, pentagon, hexagon, heptagon and octagon.
 7. The fan structure according to claim 1, wherein the blade includes a first surface and a second surface opposite to the first surface, the polygonal dents are provided on the first surface and the second surface. 